Carbon composite structure including a band of helically wound carbon fibers

ABSTRACT

A substantially all-carbon planar structure is provided which comprises essentially continues carbon fibers in a carbonaceous matrix. The fibers in the region adjacent to the periphery of the structure are ordered in a direction which substantially follows the contour of the periphery thereby providing increased strength against stresses in the region adjacent to the periphery. The fibers in the remainder of the structure may or may not be ordered.

United States Patent Spain I Feb. 1,1972

[54] CARBON COMPOSITE STRUCTURE INCLUDING A BAND OF HELICALLY WOUNDCARBON FIBERS [72] Inventor: Raymond G. Spain, Raleigh, N.C.

[73] Assignee: Monsanto Company, St. Louis, Mo.

[22] Filed: Oct. 8, 1969 211 App1.No.: 866,116

[52] U.S.Cl ..161/35, 156/169, 161/42, l6l/149,l88/257, 192/107 [51]Int. Cl. ..D04h 3/02 [58] Field of Search ..l6l/42, 44,170, 182, 35,DIG. 4, 161/86, 149; 188/251, 251 M, 251A; 192/107;

[56] References Cited UNITED STATES PATENTS 3,072,558 1/1963 Myers eta1. ...204/280 3,107,152 10/1963 Ford et a1 2,728,701 12/1955 Wirth3,552,533 l/197l Solon et a1 3,473,637 10/1969 Rutt ..l92/l07 X PrimaryExaminer-Philip Dier Attorney-Vance A. Smith, Russell Weinkauf, John DvUpham and Neal E. Willis [5 7] ABSTRACT A substantially all carbonplanar structure is provided which comprises essentially continuescarbon fibers in a carbonaceous matrix. The fibers in the regionadjacent to the periphery of the structure are ordered in a directionwhich substantially follows the contour of the periphery therebyproviding increased strength against stresses in the region ad jacent tothe periphery. The fibers in the remainder of the structure may or maynot be ordered.

4 Claims, 4 Drawing Figures PATENTEU FEB 1 I97? SHEET 1 [IF 2 FIG. I.

INVENTOR. RAYMOND G. SPAIN ATD'TORE CARBON COMPOSITE STRUCTURE INCLUDINGA BAND OF HELICALLY WOUND CARBON FIBERS FIELD OF THE INVENTION Thepresent invention relates to a composite structure having improvedstrength in the peripheral regions thereof and a method of fabricatingthe same. More particularly, this invention relates to an essentiallyplanar all-carbon, composite, structure having improved strength in theperipheral regions thereof and a method of fabricating the same.

BACKGROUND OF INVENTION Due'to the increased size and landing speeds ofmodern aircraft, much emphasis is being placed upon the development ofsuperior brakes to reduce the motion of the aircraft. Aircraftordinarily employ disc brakes which function much like those of apedal-actuated bicycle brake consisting of a stack of alternating rotorsand stators. The rotors and stators having splined peripheral regionsare coupled to the wheel and axle respectively. When the members arepressed together, the motion of the aircraft is reduced due to thefrictional force of the friction elements attached or positioned betweenand against the rotor and stators. Simultaneously, a large amount ofenergy is released as heat, and a large stress is created in the splinedareas of the rotors and stators. The splined areas are ordinarilylocated along the outer periphery of the rotor and the inner peripheryof the stator.

Present developments are focusing upon various materials which canwithstand both the stress and the deleterious effects caused by thegeneration of heat. A material which has shown considerable promise isan all-carbon composite. Recent evaluation, however, of all-carboncomposites based upon laminated carbon or graphite cloth have shown thatthe interlaminar strength of the disc has not been entirelysatisfactory, particularly in the splined regions of the discs. Besidesfailure through breakage, such discs also have a tendency to failthrough delamination in the splined region.

It is therefore a primary object of the present invention to provide'anessentially planar, all-carbon, composite structure with improvedstrength in the peripheral regions thereof.

BRIEF STATEMENT OF THE INVENTION Briefly, in accordancewith the presentinvention, 1 provide an essentially planar, substantially all-carbon,composite structure which is to be utilized under conditions whichsubject the peripheral regions thereof to high stresses. The planarstructure comprises carbon fibers in a carbonaceous matrix. As usedherein, matrix defines a constituent of a composite which surrounds theother composite elements, such as fiber reinforcement components, andacts or has acted as a cementing medium. The fibers are essentiallycontinuous in the peripheral regions subject to the high stresses andhave an or dered direction" which substantially follows the contour ofthe periphery of the planar structure. I have found that the structureas stated above has greatly improved stress capacity along the plane ofthe planar structure and also has increased resistance to delamination.

The expression ordered direction as employed herein is intended to coverthe general orientation of the fibers. Although the fibers do cross oneanother, the general and predominant direction in which the fiber pathsextend is along the contour of the periphery of the planar structure.The term planar structure itself is meant to include those structureshaving a thickness dimension along a line normal to the major or planarsurfaces thereof which is small compared with the transverse dimensionacross the faces or major surfaces. The term periphery is employed inits general meaning. That is, it is the permeter or circumference of aplanar structure. In the case of specific planar structures such as, forexample, an annular planar disc, both the other and inner perimeter areconstrued herein as the periphery.

DESCRIPTION OF THE DRAWINGS The features of the present invention whichI desire to pro tect are pointed out with particularity in the appendingclaims. The invention itself, together with further objects and advantages thereof, may be best understood with reference to the followingdescription taken in connection with the appended drawings in which:

FIG. l is a simplified vertical view, partly in section, of a typicalaircraft brake system.

FIG. 2 is a plan view ofa rotor element having a structure in accordancewith one embodiment of the present invention.

FIG. 3 is a perspective view of the rotor element of FIG. 2.

FIG. 4 is a plan view of a stator element having a structure inaccordance with another embodiment of the present invention.

DESCRIPTION For purposes of clarity and simplicity, the followingdescriptive matter discusses the utility of my present invention inturns of a pressure-actuated brake assembly with rotors and stators.Referring now to FIG. 1 which illustrates a simplified aircraft brakeassembly, it is shown therein a horizontal axle 10 to which a wheel 11is appropriately journaled through roller bearings 12 (only one of whichis shown). The brake as sembly portion comprises (I) a plurality ofannular discshaped rotor members 13 which are keyed or splined to wheel11 via member 14 and (II) a plurality of annular disc'shaped statormembers 15 which are keyed or splined to the stationary axle 10 viamember 16.

Each of the rotor members 13 and stator members 15 is pro videdrespectively with a pair of rotor frictional elements 17 and statorfrictional elements 18.

Elements l7 and 18 are respectively positioned against the oppositefaces of rotors l3 and stator 1.5 which in turn are adapted to becompressed against backplate 19 via a hydraulically actuated pressuremechanism or other appropriate means (not shown).

FIG. 2 is a plan view illustration of a rotor frictional element 20which may be utilized in the apparatus described in FIG. 1. Rotorfrictional element 20 is an annular disc having six splines 21 along theouter circumference or periphery thereof. Splines 21 function to coupleelement 20 to wheel 11 by means of axle 10 (as seen in FIG. 1).

When the brake assembly of which rotor frictional element 20 is a partis actuated, element 20 is pressed tightly against an adjacent statorfriction element to provide the frictional force needed to reduce therotational speed of the wheel and, therefore, the aircraft. Thefrictional surface area is inside the re gion encompassed by the rootdiameter of splines 21. Thus, because the driving force (see referencenumeral 22) is acting in a direction tangential to element 20 and thefrictional force (reference numeral 23) is acting in the oppositedirection, large stresses are developed in the region of splines 21. Itis therefore imperative that frictional element 20 comprise materialswhich are able to withstand the stresses which develop in the disc.

Rotor frictional element 20 is comprised of an essentially all-carboncomposite which includes continuous carbon or graphite fibers (carbonbeing employed hereinafter as generic to both) in a carbonaceous matrix.To better illustrate the fibrous nature of element 20, the fiberstherein are greatly exaggerated via heavy lines. The carbon fibers, atleast in the regions adjacent splines 21, have an ordered directionwhich follows the contour of the splined periphery of element 20. Thefiber continuity and designated ordered direction provide increasedstrength when compared to similar elements made with laminar orall-staple-fiber-constructed composites. As is explained hereinafter,the continuous fiber path crosses due to the winding technique employedin fabrication. The crossing insures that delamination does not occurunder stress as in laminated structures.

To better illustrate the ordered direction of the continuous carbonfibers, rotor element is shown in perspective in FIG. 3. For clarity,the carbon fiber has not been drawn in regions other than the one nearthe periphery of element 20. It is evident from FIG. 3 that the carbonfiber essentially follows the contour of rotor 20 and also crosses overat many positions.

FIG. 4 is an illustration of a stator frictional element 30 which alsomay be utilized in the brake assembly of FIG. 1. As seen in FIG. 4element 30 is an annular disc having six splines 31 located on the innerperiphery thereof. It should be un derstood that the number of splinesis purely a matter of choice. The construction of element 30 is inaccordance with another embodiment of my present invention wherein thecontinuous fibers are utilized only in the region 32 adjacent splines31. The remaining regions removed from splines 31 are comprised of otherfiber configurations such as, for example, a randomly oriented shortcarbon fiber staple composite. As before, the continuous fibers sweepabout splines 31 in an ordered direction which essentially follows thecontour of the splined inner periphery thereby strengthening theseregions against stress.

As stated above, the stators and rotors alone may establish thenecessary friction for causing the aircraft to decelerate, or frictionalelements may be inserted therebetween. Alternatively, however, africtional surface may be applied-to both elements in the frictionregions which are inside the splined region in the case of the rotorsand outside the splined region in the case of stators. For example, theregion designated by reference numeral 33 in FIG. 4 may be recessed andthen filled with appropriate frictional material which has a differentfrictional behavior i.e., different coefficient of friction) than thecarbon composite.

It should also be noted that the materials utilized as the matrix may beof any carbonaceous material or material which yields a carbonaceousresidue upon high-temperature pyrolysis. An example of such a matrixmaterial is a phenolic resin containing dispersed particulate carbon orgraphite.

EXAMPLE To more completely describe the present invention, reference isnow made to the following example which illustrates a technique offabricating the structure of my present invention.

This example is directed toward the construction and testing of arotating disc, i.e., a rotor utilized in a frictional brake assembly.Initially a Carbon fiber such as, for example, that obtainable fromHitco Materials, Division of H. L. Thompson Company, Gardena, Calif.,under the stock designation HMG- 50, is coated with a resin materialcontaining powdered graphite to give a resin fiber powdered-graphiteweight ratio of about 40:45:15. The resin solution may be any resinsolution which yields a carbonaceous residue upon pyrolysis. Forexample, I have found it convenient to utilize a solution comprised ofthe following: materials approximately 64.5 percent by weight of aphenolic varnish, 12.4 percent by weight of a particulate carboncomposition such as graphite powder stock designation SW 1,651(from theSouth West Graphite Co., Burnett, Tex.); and methylethyl ketone ofapproximately 23.1 percent by weight. The ketone acts as thinner to givethe solution a workable consistency.

The coated fiber is fed to a rotating cylindrical mandrel at anappropriate speed, e.g., 100 feet per minute. It is preferred, asexplained below, that the fiber be wound helically across the drum aswell as around the circumference thereof. To ensure that the resin doesnot adhere to the mandrel, it is convenient to cover the mandrel with anappropriate release paper prior to winding.

Removing the solvent is accomplished by drying the resinfiber band onthe mandrel while rotating slowly in air at room temperature. Anyresidual solvent may be removed by placing the band in an oven at about150 F. for several hours and by placing the resin-fiber band in a vacuumat room temperature for several hours.

The band is removed from the mandrel, heated to a softened state, andforced into a preform. The preform has the same general shape as thefinal splined peripheral shape of the desired article, e.g., a statorhaving splines about the inner periphery. The remaining volume of thepreform is filled with an appropriate mixture of fiber, powderedgraphite (particulate carbon), and resin (yielding a carbonaceousresidue upon pyrolysis). It should be noted at this point that theentire volume may be filled with continuous fiber-resin mixture or aresin particulate-carbon mixture when desired instead of using a staplefiber-resin mixture.

The now substantially planar preform-shaped article is inserted into amold having the final desired shape, and a force generating a pressureon the order of 3,000 pounds/square inch is applied in an axialdirection to the windings. That is, the force is applied normal to therotational plane(s) of the winding when on the rotating mandrel. This isnecessary in order that winding in the final state will have the desiredpreferred direction.

It is preferred that the preform-shaped article be made with a smallerouter diameter and, when annularly shaped, a larger internal diameterthan the mold to facilitate placement of the article therein. The axialpressure imposed against the article causes it to fill the final moldand closely follow the contours thereof. The carbon fibers arepractically inelastic and must of necessity possess some freedom ofmovement in order that the band may readily follow the contours of thepreform mold and subsequently the final mold. By helically orsinuisoidally winding the fiber on the rotating mandrel, a geometricconfiguration of winding is preferred which permits the needed fibermovement during molding.

The molded article is pyrolized at approximately 1,800" C. for about 8hours until the article becomes an essentially allcarbon composite 99percent carbon or greater). To ensure that porosity resulting fromshrinkage is minimized, the molding article may be repeatedlyreimpregnated with, for example, furfuryl alcohol and then repyrolyzed.

To illustrate the comparative strength of a disc constructed inaccordance with my present invention, a test was conducted on theultimate strengths in the splined regions of an all-carbon compositerotor having only staple fibers, a laminated woven carbon fabric rotor,and a rotor in accordance with the present invention. A hydraulicallyactuated metal bar was placed against a spline of a rigidly held rotor,and a force was applied tangential to the rotor. At a force whichcreated a pressure of 1,200 lbs/m the spline of the carbon staple rotorbroke. The woven carbon rotor broke at a pressure of 3,000 lbs./in. Incontrast thereof, a rotor constructed in accordance with the presentinvention remained integral under pressures of 3,000 lbs./in. and above.

In light of the foregoing, it should be readily appreciated that theadvantages and objectives as set forth hereinbefore are readily attainedthrough a planar frictional device and fabrication technique inaccordance with my present invention. The increased strength in theperipheral regions of a substantially all-carbonaceous matrix isprovided by the presence of continuous high-tensile-strength carbonfibers having an ordered direction which essentially follows the contourof the periphery of the planar frictional device. Thus, the planarfrictional device is useful not only in frictional brakes as described,but in any mechanism which experiences high stresses such as, forexample, a disc-type clutch.

While the invention has been set forth with respect to certainembodiments and specific examples thereof, many modifications andchanges will readily occur to those skilled in the art. Accordingly, bythe appended claims, I intend to cover all such modifications andchanges which fall within the true spirit of the present invention.

lclaim:

l. A substantially all-carbon composite annular disc having splinesalong one periphery thereof, said disc comprising a outer periphery ofsaid annular disc.

3. The disc of claim 1 wherein said one periphery is the inner peripheryof said annular disc.

4. The disc of claim 1 in which a material having different 5 frictionalcharacteristics from said all-carbon composite is secured to the planarsurfaces of said disc.

CERTIFICATE OF CORRECTION Patent No Dated February 1,

l fl Raymond G. Spain It is certified that error appears in theabove-identified patent and that said Letters Patent are herebycorrected as shown below:

- "1 Please correct the patent to show that it was assigned to TheBendix Corporation instead of Monsanto in accordance with the Assignmentwhich was recorded August 11, 1971 at Reel 2754 and Frame 509 Signed andsealed this 13th day of June1972.

(SEAL) Attest EDWARD M.FLETCHER, JR. ROBERT GO'I'TSCHALK AttestingOfficer Commissioner of Patents

2. The disc of claim 1 wherein said one periphery is the outer peripheryof said annular disc.
 3. The disc of claim 1 wherein said one peripheryis the inner periphery of said annular disc.
 4. The disc of claim 1 inwhich a material having different frictional characteristics from saidall-carbon composite is secured to the planar surfaces of said disc.